linux-kernel - Re: [PATCH] RAS/CEC: replace use of system_wq with system_percpu

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Message-ID: <CAAofZF4Sdk0REJFearcrB5_MLLQZWaNpecUPV0+BOiNcvmTaWA@mail.gmail.com>
Date: Thu, 6 Nov 2025 10:17:18 +0100
From: Marco Crivellari <marco.crivellari@...e.com>
To: Borislav Petkov <bp@...en8.de>
Cc: linux-kernel@...r.kernel.org, linux-edac@...r.kernel.org, 
	Tejun Heo <tj@...nel.org>, Lai Jiangshan <jiangshanlai@...il.com>, 
	Frederic Weisbecker <frederic@...nel.org>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, 
	Michal Hocko <mhocko@...e.com>, Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH] RAS/CEC: replace use of system_wq with system_percpu_wq

On Wed, Nov 5, 2025 at 10:08 PM Borislav Petkov <bp@...en8.de> wrote:
> On Wed, Nov 05, 2025 at 05:55:49PM +0100, Marco Crivellari wrote:
> > The code is using system_wq, this is the per-cpu workqueue. This change will
> > only replace system_wq with system_percpu_wq. So the behavior is the same as
> > before.
>
> What does that mean?
>
> We're going away from system_wq in favor or system_percpu_wq? Or?
>


It's just a "rename" from system_wq to system_percpu_wq.
system_percpu_wq is a per-cpu workqueue, exactly as system_wq.

But in a few release cycles system_wq will be removed from the code.

If you want to have more details, you can read this discussion:

https://lore.kernel.org/all/20250221112003.1dSuoGyc@linutronix.de/

> It is not clear to me what the issue is what the new correct way should be...

There is no issue, except that system_wq will be removed. In order to
achieve the same result as system_wq, the correct workqueue to use
is system_percpu_wq.

As you can see from:

commit 128ea9f6ccfb ("workqueue: Add system_percpu_wq and system_dfl_wq")

system_percpu_wq is defined as a per-cpu workqueue, exactly as system_wq.

Thanks!

-- 

Marco Crivellari

L3 Support Engineer, Technology & Product